The purpose of this project is to further develop and define as fully as possible a pure strain of large dogs for medical research with an ultimate goal of breeding and making available a histocompatible dog. The existing colony of 300 purebred Labrador retrievers and 20 inbred beagles will be utilized for this study. Ongoing studies will be continued. These include studies to determine optimum methods of husbandry, costs of producing dogs, causes of puppy mortality, normal physiological and biochemical parameters, the best means of computerized record keeping, the inheritance of congenital defects, optimum methods of semen preservation and artificial insemination, the inheritance of behavioral traits, the prevalance and inheritance of blood types, the inheritance of fertility, and the degree of similarity of dogs in the colony as determined by cytotoxicity and one-way lymphocyte stimulation tissue typing in vitro. New extensions of these studies will include a systematic search for new lymphoctye antigens and the development of reasonable monospecific antisera, a systematic search for new red cell antigens and the development of antisera, the determination of the inheritance of the major histocompatibility locus in the dog, transplantation of skin and organs to determine the degree of histocompatibility attained in the colony and establishing immunologic parameters in neonate and mature dogs.